A conventional tape transport device, such as the tape transport device used in a magnetic tape recorder/player 10, is schematically depicted in FIG. 1. Tape 11, which is supplied from a supply reel 12, is fed between a capstan 13 and pinch roller 14 assembly to a take up reel 15. In the operation of the recorder/player, the tape 11 is fed at varying speeds between the reels 12, 15. For normal speeds, and speeds up to approximately twenty times normal, the tape 11 is advanced by a capstan motor 16 connected to the capstan-pinch roller assembly 13-14. Such speeds are considered low operating speeds.
When using the capstan-pinch roller assembly 13-14 to advance the tape 11, the tape speed remains relatively constant. When it is desired to advance the tape 11 at a high speed, such as 100 to 200 times the normal speed, the capstan-pinch roller assembly 13-14 is not used. Rather, the tape 11 is typically advanced at high speeds by a drive mechanism connected to one of the reels 12 or 15.
In the prior art, the tape advance rate at high speeds was kept constant by maintaining a certain relationship between the rotational periods of the supply and take-up reels. In FIG. 2, a cross-sectional segment of the tape 11 is shown having a thickness t. The tape itself has a total length L and L&gt;&gt;t. Assuming that the length L and thickness t are uniform and unchanging in FIG. 1, the tape has a fixed cross-sectional area of Lt. Further, this area must be constant at any given moment regardless of how much tape is wound on each reel. If at a particular moment, the outer radius of the supply reel is r.sub.S and the outer radius of the take up reel is r.sub.T (each reel having a minimum inner radius of r), then the following equation relates the areas of tape on each reel to the total cross-sectional area: EQU .pi.(r.sub.T.sup.2 -r.sup.2)+.pi.(r.sub.S.sup.2 -r.sup.2)=Lt(1)
because the amount of tape between the reels is negligible. Further, if the rotational period of the take-up and supply reels are represented by T.sub.T and T.sub.S, respectively, then the following relationship is also true: ##EQU1## where V.sub.T is the tape speed. Equations (1) and (2) can be combined to yield: ##EQU2## An examination of the right hand side of equation (3) reveals that only the terms in the denominator vary as tape is transported from one reel to another. Hence, the prior art attempted to maintain the constancy of the high speed tape advance by maintaining a constant relationship between the sum of the squares of the rotational periods or the sum of the rotational periods of the reels.
This solution proves problematic for the conventional tape player/recorder. As noted above, the speed of a particular tape is a function of both the thickness and length (e.g., 30, 60 90, 120, etc. minutes) of the tape. Since a conventional tape player/recorder accepts tapes with varying lengths and thicknesses, the constancy of higher advance speeds cannot easily be maintained universally for all tapes.
It is therefore an object of the present invention to provide a high speed controller which maintains the tape advance at a constant rate. It is a further object to provide a constant tape speed controller which uniformly maintains a constant tape speed regardless of the length or thickness of the tape used in the playback/recorder.